Folding, or interfolding, unit of a web, or sheet, of paper in a paper converting machine

ABSTRACT

Folding or interfolding unit of a web, or sheet, of paper, comprising a first and a second folding or interfolding roll, of a web, or sheet, of paper, configured to fold or interfold, the web or sheet of paper according to a predetermined folding or interfolding configuration, at a folding or interfolding zone arranged between the first and the second folding or interfolding roll. The folding or interfolding unit comprise, furthermore, a first and a second plurality of detaching fingers configured to cause the web or sheet of paper to be detached from the external surface of the respective folding or interfolding roll.

FIELD OF THE INVENTION

The present invention relates to the technical field of paper converting, and similar products, and, in particular, relates to a machine for interfolding a web, or sheet, of paper.

The invention, furthermore, relates to a method for folding or interfolding a web or sheet of paper according to a determined interfolding configuration.

DESCRIPTION OF THE PRIOR ART

As it is known, in the paper industry many machines and processes are used for producing paper tissues, towels, and similar products in stacks of interfolded sheets having a determined height. These are produced folding the sheets in an interfolded way that means closing at each fold a final edge of the previous sheet and a starting edge of the following sheet.

In this way, at the moment of using the product, when a sheet is extracted from the stack, also an initial edge of the following sheet is extracted, thus simplifying its use for some kinds of uses.

The interfolding machines of known type work one, or more, webs of paper coming from one, or more reels that are cut at a cutting unit, in sheets of predetermined length and staggered fed to a folding unit at which 2 counter-rotating folding rolls work. More precisely, the cut in sheets of the webs is carried out on cutting rolls which alternately cooperate with related counter-blades.

Among the possible ways to fold the sheets, are known, in particular, the “L” interfolded, with 2 panels, the “Z” interfolded, with 3 panels, and the “W” interfolded, with 4 panels.

In the case of “L” interfolded, obtained by “single-fold” machines, of the type that is for example described in U.S. Pat. No. 6,228,014, the webs of paper are cut in such a way to form two staggered sequences of sheets which are alternately fed to the folding rolls. In this way, each sheet coming from a first direction is superimposed, for about half sheet, to a portion of the sheet coming from a second direction, and vice versa, at the moment in which the fold is carried out.

In the case of “Z”, “W”, interfolded, or even more panels, obtained by “multi-fold” machines of known type, for example described in U.S. Pat. No. 3,490,762, only one web of paper is processed and to the folding rolls, a sequence of sheets comes only from one direction that are already partially superimposed to each other. As described in EP1520822, the superimposition between two following sheets is carried out immediately after the cut by a transfer roll and a delay roll, which together generate a small fold in a previous sheet under which the following sheet is in part positioned.

Both in the single-fold and in the multi-fold machines, the folding rolls have a circumference whose length is a multiple of the panel length. In particular, in order to fold or interfold the sheets, the folding rolls are provided with retaining devices, such as suction holes, or mechanical pliers, which are synchronously activated for alternately starting and finishing each fold between two following panels.

For example, as described in EP1457444B1 a folding or interfolding unit comprises, normally, a first folding or interfolding roll, which keeps the web or sheet of paper for a determined angular distance by a determined suction system comprising a determined number of longitudinal rows of suction holes, and then “passes” the sheet to a second folding or interfolding roll, also this provided with a vacuum distribution device symmetric to that of the first suction roll, and which works for another predetermined angular distance. This controlled “passage” of the sheet of web of paper from a folding roll to another one allows to obtain the desired folding or interfolding configuration of a stack of interfolded or folded sheets. The folding or interfolding unit provides, normally, also a first and a second plurality of “detaching” fingers moved in phase with respect to the respective folding rolls to cause the detachment of the sheets from the respective external surface. Separation members are, furthermore, provided to separate a finished stack of interfolded sheets from the following stack to be formed. Both the detaching fingers and the separator members are, normally, moved within respective grooves peripherally made in the folding rolls.

However, the folding unit described in EP1457444B1, as well as other analogous folding rolls, has some drawbacks.

In particular, the advancement of the processed web or sheet of paper along the machine on which the suction roll described in EP1457444 is mounted, as well as analogous suction rolls, cannot exceed a predetermined threshold value of the advancement speed, normally about 150÷200 m/min, value that is imposed by constructional and functional limits of determined components of the machine.

The aforementioned values of the advancement speed of the paper along the machine are also used, together with the path to be followed, to design the detaching fingers, in particular the oscillatory motion of these, and the suction roll, in particular positioning the sealing members at predetermined angular positions. Instead, if the aforementioned values of the speed used for designing the suction roll, are not respected, during the functioning of the machine, drawbacks of different kind can occur.

In particular, if the aforementioned threshold values are exceeded, due to the inertia of the paper, the processed web or sheet remains adhered to the surface of the suction roll also after the second angular position, i.e. to a portion of the surface positioned downstream of the second sealing member. This causes an advancement of the web or sheet of paper that is not accurate through the different sections of the machine and further to unavoidably compromise the quality of the final product, in particular forming unwanted folds, can cause also jamming of the paper which make it necessary to stop the machine in order to remove the jammed paper with consequent loss of time and productivity.

Therefore, in order to avoid the aforementioned drawbacks it is necessary to work at a slow speed thus reducing the productivity of the machine.

Analogous drawbacks also occur in the prior art machines in the case that the web or sheet of paper to be processed has a paper weight different from a predefined paper weight on the basis of which the folding or interfolding rolls are designed. In fact, due to the greater inertia that a paper with a higher weight has with respect to a paper with a smaller paper weight, if a web or sheet of paper is processed that has a paper weight higher than a predefined paper weight, the web or sheet of paper remains adhered to the folding or interfolding roll, beyond the predetermined releasing point, with the aforementioned drawbacks. In general, the webs or sheets of paper with a higher paper weight cover a longer path also after the end of the suction by the roll due to the higher inertia thus causing the aforementioned functional problems and of loss of quality of the final product. Therefore, the prior art machines equipped with folding or interfolding rolls, in addition to have a low productivity, are rigid because are not able to work webs, or sheets of paper with different paper weights.

Examples of folding or interfolding rolls with the aforementioned drawbacks are described in WO2010/140046, WO2019/149905 and WO2018/019679.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a folding or interfolding unit that is able to overcome the aforementioned drawbacks of the prior art folding or interfolding rolls, in particular of the type provided with suction holes.

It is, in particular, object of the present invention to provide a folding or interfolding unit, which is able to avoid wrinkles, or “creases”, on the processed sheets and, therefore, to guarantee the obtainment of a final product of excellent quality even if a high advancement speed of the web or sheet of paper along the machine, in particular higher than 300 m/min is used.

It is also object of the present invention to provide a method for folding or interfolding a web or sheet of paper in a paper converting machine having the aforementioned advantages with respect to the prior art methods.

These and other objects are achieved by a folding or interfolding unit of a web, or sheet, of paper, comprising:

-   -   a first and a second folding or interfolding roll of a web or         sheet of paper configured to fold or interfold said web or sheet         of paper according to a predetermined folding or interfolding         configuration, at a folding or interfolding zone (35) arranged         between said first and second folding or interfolding rolls;     -   a first and a second plurality of detaching fingers configured         to cause said web or sheet of paper to be detached from an         external lateral surface of the respective folding or         interfolding roll;     -   a first and a second actuation group configured, respectively,         to cause a back-and-forth oscillatory motion of said first and         second pluralities of detaching fingers towards/from said         folding or interfolding zone, in such a way to cause a         respective web or sheet of paper to be detached, respectively,         from said first and second folding or interfolding roll;     -   whose main characteristic is that said first and second         actuation groups are, furthermore, configured to postpone or         anticipate, said oscillatory motion of said first and of said         second plurality of detaching fingers with respect to a         predetermined reference oscillatory motion, in such a way to         postpone or anticipate, the instant (tr) in which said first and         second plurality of detaching fingers are arranged to cause the         detachment of said web or sheet of paper respectively from said         first and second folding or interfolding roll.

Other technical characteristics of the present invention are defined in the dependent claims.

According to another aspect of the invention, a method for folding or interfolding, a web or sheet of paper in a paper converting machine comprising the steps of:

-   -   feeding at least one web or sheet of paper along a predetermined         advancing direction;     -   folding, or interfolding, said web or sheet of paper at a         predetermined folding or interfolding zone of a paper converting         machine, said folding or interfolding step, being carried out by         a first and a second folding or interfolding roll between which         said folding or interfolding zone is defined;     -   detaching by a first and a second plurality of detaching fingers         said web or sheet of paper from the external lateral surface of         the respective folding or interfolding roll, said step of         detaching being obtained causing a back-and-forth oscillatory         motion of said first and second plurality of detaching fingers         towards/from said folding or interfolding zone;         whose main characteristic is that an adjustment step is,         furthermore, provided to adjust the phase between said first and         second pluralities of detaching fingers and said first and         second folding or interfolding rolls, respectively, said         adjustment step being arranged to postpone or anticipate, said         oscillatory motion of said first and of said second plurality of         detaching fingers.

In particular, the adjustment step is atta a delay or anticipate, the oscillatory motion of the first and of the second plurality of detaching fingers with respect to a predetermined reference oscillatory motion. More in particular, the aforementioned reference oscillatory motion is arranged to cause the detachment of the web or sheet of paper from the respective folding roll at a predetermined realising reference instant tr*.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be shown with the following description of its exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings in which:

FIG. 1 diagrammatically shows a side elevation view of a first embodiment of a folding or interfolding unit according to the invention;

FIGS. 2 and 3 diagrammatically show side elevation views of possible alternative embodiments of the folding or interfolding unit of FIG. 1 ;

FIG. 4 diagrammatically shows a side elevation view of a first embodiment of a folding or interfolding roll, according to the invention;

FIGS. 5 and 6 diagrammatically show transversal cross section views of a first embodiment of a folding or interfolding roll, according to the invention, respectively in the catching instant, and in the releasing instant of a web or sheet of paper;

FIGS. 7 and 8 diagrammatically show, respectively, a side elevation view and a transversal cross section of a first functioning mode of the folding or interfolding roll, according to the invention;

FIG. 9 shows an enlargement of a portion of FIG. 8 to diagrammatically show some aspects of the first functioning mode of the folding or interfolding roll according to the invention;

FIGS. 10 and 11 diagrammatically show, respectively, a side elevation view and a transversal cross section of a second functioning mode of the folding or interfolding roll, according to the invention;

FIG. 12 shows an enlargement of a portion of FIG. 11 to diagrammatically show some aspects of the second functioning mode of the folding or interfolding roll according to the invention;

FIG. 13 diagrammatically shows a longitudinal cross section view of an alternative embodiment according to the invention for the folding or interfolding roll of FIG. 4 ;

FIG. 14 diagrammatically shows the alternative embodiment of FIG. 13 of the folding or interfolding roll a side elevation view;

FIGS. 15 and 16 show, respectively in a side view and in a transversal cross section, of a first functioning mode of the folding or interfolding roll of FIGS. 13 and 14 ;

FIGS. 17 and 18 show, respectively in a side view and in a transversal cross section, a second functioning mode of the folding or interfolding roll of FIGS. 13 and 14 ;

FIGS. 19 and 21 show transverse cross section views of other possible alternative embodiments of the roll of FIGS. 13 and 14 according to the invention;

FIG. 20 shows an enlargement of a portion of FIG. 19 to highlight some technical characteristics;

FIG. 22 shows a side elevation view of another alternative embodiment according to the invention for the folding or interfolding roll of FIG. 4 ;

FIG. 23 diagrammatically shows a side elevation view of a possible embodiment of a paper converting machine which uses the folding or interfolding unit according to the invention.

DETAILED DESCRIPTION OF SOME EXEMPLARY EMBODIMENTS OF THE INVENTION

As diagrammatically shown in FIG. 1 , a folding or interfolding unit 150, according to the invention comprises a first and a second folding or interfolding roll 1 a and 1 b. In particular, the first and second folding or interfolding rolls 1 a and 1 b are configured to fold or interfold the web or sheet of paper according to a predetermined folding or interfolding configuration, at a folding or interfolding zone 35 defined between them.

In addition to the first and second folding or interfolding rolls 1 a and 1 b, the folding or interfolding unit 150 comprises a first and a second plurality of detaching fingers 40 a and 40 b arranged to operate in phase, respectively, with the first and the second folding or interfolding roll 1 a and 1 b to detach a respective web or sheet of paper 5 from surface 11 of a respective tubular body 10 a and 10 b of the first and of the second folding or interfolding roll 1 a and 1 b, in such a way to form a stack 250 of folded or interfolded sheets.

In particular, a first and a second actuation group 80 a and 80 b can be provided configured, respectively, to cause a back-and-forth oscillatory motion of the first and of the second plurality of detaching fingers 40 a, and 40 b towards/from the aforementioned folding or interfolding zone 35. In particular, the first and the second actuation group 80 a and 80 b, are, furthermore, configured to postpone or anticipate the oscillatory motion of the first and of the second plurality of detaching fingers 40 a, and 40 b with respect to a predetermined reference oscillatory motion, in such a way to postpone or anticipate, the instant tr in which the first and the second plurality of detaching fingers 40 a and 40 b are arranged to cause the web or sheet of paper 5 to be detached from the respective folding or interfolding roll 1 a and 1 b, in particular with respect to a predetermined reference realising instant tr*.

In particular, in a first embodiment diagrammatically shown in FIG. 1 , the first and the second actuation group 80 a and 80 b can comprise, respectively, a first and a second actuation device 91 a and 91 b. More in particular, the first and the second actuation device 91 a and 91 b are provided, respectively, with a first and with a second motor group 85 a, 85 b. These are, respectively, operatively connected to a first and to a second motor shaft 86 a, and 86 b. More precisely, the first and second motor groups 85 a and 85 b are arranged to cause a rotation of the first and of the second motor shaft 86 a and 86 b about respective axes of rotation 185 a and 185 b.

In particular, the first and the second actuation group 80 a and 80 b can comprise, respectively, a first and a second oscillator device 90 a, 90 b configured to convert the rotational motion on an inlet axis, or power take-off, to an oscillatory motion on an outlet axis, or power take-off.

The oscillator device of mechanical type can be a device of known type to the skilled person in the art and will not be described in detail here.

Preferably, the first oscillator device 90 a and the second oscillator device 90 b, for example a first and a second mechanical oscillator, can comprise respectively a first and a second mechanical cam, preferably a first and a second desmodromic cam, not shown in the figure for simplicity reasons.

In particular, the first and the second motor shaft 86 a and 86 b can be connected at the inlet to the first and to the second oscillator device 90 a and 90 b. These, advantageously, comprise outlet shafts 83 a and 83 b, respectively, connected to a first and a second transmission group 81 a and 81 b arranged to transmit the oscillatory motion to the first and to the second plurality of detaching fingers 40 a and 40 b. In particular, the aforementioned outlet shafts 83 a and 83 b are connected to the first and to the second transmission group 81 a and 81 b by a respective mechanical cam 84 a, and 84 b, advantageously a desmodromic cam, case that is not shown in the figures for clarity reasons.

In this way, it is possible to obtain the phase between the first and the second plurality of detaching fingers 40 a and 40 b and the other parts of the machine 100, in particular with respect to the first and second folding or interfolding roll 1 a and 1 b, causing the first and the second motor group 85 a and 85 b to rotate at a determined speed.

In particular, with respect to the prior art solutions, in particular of WO2010/140046, that provide a crank and connecting rod mechanism to convert the rotational motion to an oscillatory motion, the solution provided by the present invention is able to guarantee a greater accuracy. In particular, the solution provided by the present invention allows to very accurately adjust the phase between the detaching fingers 40 a and 40 b and the respective rolls 1 a and 1 b, in particular to anticipate, or postpone, the oscillatory motion, respectively, of the first and of the second plurality of detaching fingers 40 a and 40 b with respect to a predetermined reference oscillatory motion.

Advantageously, it is possible to adjust the phase of the detaching fingers 40 a and 40 b, i.e. postpone or anticipate the oscillatory motion with respect to the other mechanical organs of the machine 100, slackening, or accelerating, for the necessary period of time, the first and the second motor group 85 a and 85 b. In other words, starting from a predetermined reference condition, in which the first and the second motor group 85 a and 85 b rotate at a reference speed vm*, the first and the second motor group 80 a and 85 b are slacken, or accelerated for an interval of time Δt*, and then their speeds are brought back to the reference speed vm*. In particular, it is possible to increase, or decrease, for a determined period of time, the speed of rotation of the first and of the second shaft of rotation 86 a, 86 b, with respect to the set reference speed vm*, in such a way to anticipate, or postpone, respectively, the oscillatory motion of the first and of the second plurality of detaching fingers 40 a, and 40 b, in particular with respect to a reference oscillatory motion. In particular, in the way described above it is possible to accelerate or decelerate the oscillatory motion of the detaching fingers 40 a and 40 b.

Also in the alternative embodiment diagrammatically shown in FIG. 2 , the first and second actuation groups 80 a and 80 b comprise, respectively, a first and a second motor group 85 a and 85 b arranged to cause the rotation of a first and of a second motor shaft 86 a, and 86 b about respective axes of rotation 185 a and 185 b. Furthermore, also in this case, a first and a second oscillator device 90 a and 90 b, preferably of mechanical type, are provided, arranged to convert the rotational motion of the motor shaft 86 a and 86 b to an oscillatory motion, and a first and a second transmission group 81 a and 81 b arranged to transmit the oscillatory motion at the outlet of the first and of the second oscillator device 90 a and 90 b, respectively, to the first and to the second plurality of detaching fingers 40 a, and 40 b.

In this case, however, differently from what stated above with reference to FIG. 1 , the first and second oscillator devices 90 a and 90 b are, advantageously, associated, respectively, to a first and to a second adjustment device 94 a and 94 b configured to adjust the phase of the first and second pluralities of detaching fingers 40 a and 40 b with the respective folding or interfolding rolls 1 a and 1 b. In particular, the first and the second adjustment device 94 a and 94 b are arranged to anticipate, or postpone, the instant tr in which the first and the second plurality of detaching fingers 40 a, 40 b are arranged to hit the web or sheet of paper 5 to cause the same to be detached from the respective folding or interfolding roll 1 a and 1 b.

Advantageously, the first and the second adjustment device 94 a and 94 b can comprise, respectively, a first and a second phase-shifter gearbox 95 a, and 95 b of type known to the skilled person in the art. More precisely, in this case, the first and the second phase-shifter gearbox 95 a and 95 b can be operatively connected respectively to the first and to the second motor group 85 a and 85 b, for example, by a first transmission belt 87 a and 87 b, and to a first and to a second actuation device 91 a and 91 b by a second transmission belt 88 a and 88 b. More precisely, the first and the second actuation device 91 a and 91 b are arranged to transmit the rotational motion generated dal first and dal second motor group 85 a and 85 b, respectively to the aforementioned first and second oscillator device 90 a and 90 b which convert the rotational motion to the aforementioned oscillatory motion which is transmitted to the first and the second plurality of detaching fingers 40 a and 40 b. The first and the second phase-shifter gearbox 95 a and 95 b are, respectively, provided with a first and a second electric motor 96 a and 96 b. These are arranged to adjust the speed of rotation of the first and of the second actuation device 91 a and 91 b adjusting the speed and the sense of rotation of a first and of a second epicycloidal gear, not shown for simplicity, housed, respectively, within the first and the second phase-shifter gearbox 95 a and 95 b.

In an embodiment of the invention that is not shown in the figures for clarity reasons, the first and the second oscillator device 90 a and 90 b, in any of the embodiments described above, can be connected to a respective first end 81′a and 81′b of the aforementioned first and second transmission group 81 a and 81 b operatively connected at a second end 81″a and 81″b opposite to the first end, respectively, to the first and to the second plurality of detaching fingers 40 a and 40 b. Therefore, the first and the second oscillator device 90 a and 90 b are positioned laterally, respectively, to the first and to the second plurality of detaching fingers 40 a and 40 b.

According to a possible functioning mode according to the invention, the first and the second electric motor 96 a and 96 b can be normally still in such a way not to change the phase of the detaching fingers 40 a and 40 b with respect to the rest of the machine 100, in particular to the folding rolls 1 a, 1 b. In the case that it is necessary to change the phase of the first and of the second plurality of detaching fingers 40 a and 40 b, the first and second electric motors 96 a and 96 b are operated to actuate respectively the first and the second epicycloid gear in such a way to temporarily accelerate, or decelerate the second transmission belt 88 a and 88 b. In this way, it is possible to introduce a delay or an advance in the oscillatory motion of the first and second pluralities of detaching fingers 40 a and 40 b and, therefore, to postpone, or anticipate, the instant in which the web or sheet of paper is detached from the respective folding or interfolding roll 1 a, 1 b, i.e. the instant tr in which the first and the second plurality of detaching fingers 40 a, and 40 b are arranged to cause the web or sheet of paper 5 to be detached from the respective folding or interfolding roll 1 a, and 1 b, in particular with respect to a reference detachment instant tr*.

In particular, the first and the second folding or interfolding roll, 1 a and 1 b of the folding or interfolding unit 150 described above with reference to the FIGS. 1 and 2 can be provided with members for retaining the processed web or sheet, of paper 5 of mechanical type (for example provided with mechanical pliers of known type), or of pneumatic type. In this latter case, the retaining members can provide bell-shaped vacuum distribution devices, of known type, or comprising sealing sectors of the type that is, for example, described in EP1457444B1.

As diagrammatically shown in FIG. 3 , the folding or interfolding unit 150 in addition to the aforementioned first and second actuation groups 80 a and 80 b of the detaching fingers 40 a and 40 b can provide a first and a second folding or interfolding roll 1 a and 1 b as described below.

In particular, each folding or interfolding roll 1 a, or 1 b of a web or sheet of paper, 5 fed along an advancing direction 15 in a paper converting machine, or similar products, comprises a tubular body 10 configured to rotate in a predetermined sense of rotation 110, for example clockwise, about a longitudinal rotation axis 101. More precisely, the tubular body 10 of the roll 1 a, or 1 b, is provided with an external surface 11 and with an internal lateral surface 12 put in communication with each other through a plurality of suction holes 3.

In particular, the suction holes 3 of the folding or interfolding roll 1 a, or 1 b, can be organized according to a predetermined number of suction groups, for example 2, or 3, or 4, suction groups 30, positioned in predetermined angular positions of the folding or interfolding roll 1 a, or 1 b, for example each 180°, 120°, or 90°. In general, the angular position of the suction groups 30 depends on the number of sheets 5 which can lay adjacent to each other on the external lateral surface 11 of the folding or interfolding roll 1. The circular arc arranged between a suction group 30 and the following one is equal to the length of a processed sheet 5 and, therefore, in function of the diameter of the folding or interfolding roll 1 a, or 1 b, it is possible to have two, three, four or even more suction groups 30. For example, if on the folding or interfolding roll, 1 a, or 1 b, five suction groups 30 are present, the angular distance between the suction groups 30 will be 72°. In the following examples, the folding or interfolding roll 1 provides 3 suction groups 30, each of which comprising 2 longitudinal rows of suction holes 3 close to each other. The folding or interfolding roll 1 provides, furthermore, a suction chamber 20 defined within the aforementioned tubular body 10, and pneumatically connected to a device for generating a predetermined vacuum degree, for example a vacuum pump, not shown in the figures for simplicity, but however of type known to a skilled person in the art. It is, furthermore, provided a vacuum distribution device 50 configured to selectively put into pneumatic communication the suction chamber 20 with at least one row of suction holes 3 of the aforementioned plurality, at predetermined angular positions of the tubular body 10. In this way, as known, the processed sheet or web of paper is caused to be sucked, and to adhere only at a determined portion of the external lateral surface 11 of the folding or interfolding roll 1 arranged between a catching point P1 and a releasing point P2 having determined angular positions, in particular with respect to a predetermined reference system (Xo,Yo,Zo). According to the present invention, a displacement device 70 is provided configured to move the aforementioned vacuum distribution device 50, in such a way to change the angular position at least of the releasing point P2, in particular with respect to a predetermined angular position P2* which this occupies with respect to the aforementioned predetermined reference system (Xo,Yo,Zo).

The displacement device 70 can be, advantageously, operated by a main control unit 300, for example comprising a PLC, or an industrial PC, or similar devices, (see for example FIG. 23 ). The main control unit 300 can be interfaced through a panel interface with an operator, for example of the HMI (Human Machine Interface) type, by means of which an operator can give commands and/or adjust the machine 100. The electronic control unit 300 can, for example, detect the need to adjust the catching point P1 and/or the releasing point P2 and communicate to the operator through the HMI the necessary setting. The operator, then, through the HMI, can carry out the adjustment according to the communication of the main control unit 300.

In this way, it is possible to anticipate or postpone the instant ta in which the web or sheet of paper adheres to the aforementioned external surface 11 of the folding or interfolding roll 1 a, or 1 b, and/or the instant tr in which the web or sheet of paper 5 leaves the aforementioned external surface 11 of the folding or interfolding roll 1 a, or 1 b.

In particular, the aforementioned displacement device 70 can be configured to move the aforementioned vacuum distribution device 50 as a function of at least one predetermined working parameter of the machine 100 within which the folding or interfolding roll 1 a, or 1 b is installed. For example, the aforementioned predetermined working parameter can be the advancement speed of the web or sheet of paper along the machine 100.

In this case, in particular, if the advancement speed v of the web or sheet of paper is greater than a predetermined reference value v*, or if the operative speed of the machine 150 is raised, the displacement device 70 is arranged to move the vacuum distribution device 50 in such a way to anticipate the detachment instant tr of the web or sheet of paper from the folding or interfolding roll 1 a, or 1 b. In particular, the displacement device 70 can be configured, in this case, in such a way to rotate the aforementioned vacuum distribution device 50 in the sense opposite to the aforementioned sense of rotation 110 of the folding roll, or about the rotation axis 101 (FIGS. 7 to 9 ).

Instead, if the machine 100 is foreseen to operate at an advancement speed of the paper slower than the aforementioned reference value v*, or simply if the operative speed of the machine 100 is decreased, the displacement device 70 is arranged to move the aforementioned vacuum distribution device 50 in such a way to postpone the release of the web or sheet of paper with respect to a reference condition. More precisely, the displacement device 70 will be, in this case, arranged to rotate the aforementioned vacuum distribution device 50 in the same sense of the aforementioned sense of rotation 110 of the folding roll, or about the rotation axis 101 (FIGS. 10 to 12 ).

In a preferred configuration of the invention, it is possible to rotate the vacuum distribution device 50 as a function of at least one working parameter, for example the advancement speed of the paper. In this case, the main control unit 300 can be atta a operate the displacement device 70 to cause the rotation desiderata of the vacuum distribution device 50. The main control unit 300 can operate the displacement device 70 according to a predetermined function or on the basis of algorithms computed in real time, for example self-learning algorithms or, in general, artificial intelligence algorithms.

In an alternative embodiment of the invention, it is possible to control the catching position P1 and/or the detaching position P2, alternating the angular position of the vacuum distribution device 50 between at least two predetermined angular positions. For example, the releasing position of the point P2′ of FIG. 12 can correspond to a slow advancement speed of the paper (for example comprised between 50 and 100 m/min), whilst the releasing position P2″ of FIG. 12 can correspond to a high advancement speed (for example higher than 250 m/min). In this case, a threshold value of the speed can be set beyond which the displacement device 70 can be operated to move the vacuum distribution device 50 from position P2′ to position P2″ anticipating or postponing, the detachment of the web or sheet of paper 5. The actuation command of the displacement device 70 can be directly given by the main control unit 300, or by an operator through the HMI interface.

Another working parameter of the machine 100 in function of which the displacement device 70 can be arranged to move the vacuum distribution device 50 can be the thickness s, or the paper weight, of the paper of the processed web or sheet. In particular, if the thickness of the paper is greater than a predetermined reference thickness s*, the displacement device 70 is arranged to move the vacuum distribution device 50 in such a way to anticipate the instant tr at which the web or sheet of paper is released from roll 1 with respect to the releasing reference instant tr*.

In particular, in this case, the displacement device 70 can be arranged to rotate the vacuum distribution device 50 in the sense opposite to the sense of rotation 110 of the tubular body 10 about the longitudinal axis 101. Instead, in the case that the thickness of the paper is smaller than predetermined reference thickness s*, the displacement device 70 is arranged to move the vacuum distribution device 50, in such a way to postpone the instant in which the web or sheet of paper is released from roll 1. In particular, in this case, the displacement device 70 can be arranged to rotate the vacuum distribution device 50 in a sense of rotation consistent with the sense of rotation of the tubular body 10 about the longitudinal axis 101.

In this case, it is possible to adjust the machine 100 in function of the product, i.e. in function of the characteristics of the paper which has to be processed. The displacement device 70 can be operated in a different way in function of the type of paper, or product, to be processed obtaining great advantages in terms of setting of the machine 100 during a product change. Each product, or type of paper, can correspond to specific movements of the displacement device 70, or to a specific reference value of the speed of the paper v* optimizing the position of the catching point P1 and/or of the releasing point P2 for each specific product, or type of paper.

In a preferred embodiment of the invention, the aforementioned displacement device 70 can be configured to move, in particular to rotate, the vacuum distribution device 50, in particular to postpone, or anticipate, the instant tr in which the web or sheet of paper is released from surface 11, in working conditions of the machine 100, that means during the rotation of the tubular body 10 about the aforementioned longitudinal rotation axis 101. In this way, in particular, it is possible to move the vacuum distribution device 50 in such a way to progressively follow the increase or decrease of the advancement speed of the web or sheet of paper.

In particular, in a first embodiment, the aforementioned vacuum distribution device 50 can comprise a fixed tubular body 25 coaxially mounted within the aforementioned tubular body 10. More in particular, the aforementioned fixed tubular body 25 pneumatically communicates with the device for generating a predetermined vacuum degree and is provided with at least one aperture 26. More precisely, the vacuum distribution device 50 can comprise, furthermore, a first and a second sealing member 27 a, and 27 b integral to the fixed tubular body 20 at opposite sides with respect to the, or each, aperture 26 and positioned longitudinally to tubular body 10. In particular, the displacement device 70 can be configured to cause a rotation of the fixed tubular body 25 about the aforementioned longitudinal rotation axis 101.

More in particular, as diagrammatically shown in FIG. 13 , the aforementioned displacement device 70 can be arranged to engage the fixed tubular body 25 at least at an actuation portion 75, advantageously a portion which protrudes axially from an end of the tubular body 10.

In particular, if the aim is to anticipate the releasing instant tr with respect to the reference condition tr* (broken line in FIG. 9 ), for example because the machine 100 is operated at an advancement speed of the paper higher than the reference speed, in particular to have a higher productivity, or to process a type of paper with a paper weight s lighter than a reference paper weight s*, the displacement device 70 can be arranged to rotate the fixed tubular body 25 in the sense opposite to the predetermined sense of rotation 110 of the tubular body 10. In this way, in fact, as diagrammatically shown in FIG. 9 , the releasing point P2 of the sheet of web of paper from the surface 11 of the tubular body 10, is moved upstream of the reference releasing point P2*.

Instead, if the aim is to operate the machine at a speed slower than a reference speed v*, or to process a type of paper with a paper weight higher than the reference paper weight s*, the displacement device 70 can be arranged to rotate the fixed tubular body 25 about the longitudinal rotation axis 101 in a sense of rotation consistent with the predetermined sense of rotation 110 of the tubular body 10 to postpone the releasing instant tr of the web or sheet of paper 5 with respect to the reference realising time tr* (see FIGS. 7 to 9 ). In this way, in fact, as diagrammatically shown in FIG. 9 , the releasing point P2 of the sheet of web of paper from surface 11 of the tubular body 10 is moved downstream of the reference releasing point P2*.

In an alternative embodiment of the invention, the catching point P1 and/or the releasing point P2 changes with the change of the speed of machine 100, conveniently anticipating or postponing at least one of the two instants between ta and tr in which the sheets are, respectively, retained and released from the external surface 11 of the folding or interfolding roll, 1 a, or 1 b. In this case, to anticipate, or postpone, the two instants ta or tr, advantageously, any reference is not made to a predetermined speed v* but can be the electronic control unit 300 to be configured to compute the position of the catching point P1 and/or the releasing point P2, in function of the speed of the machine 100 and to operate directly the displacement device 70, or indirectly by an operator which gives the command through the HMI device.

As diagrammatically shown in the figures from 13 to 18, and in particular in FIG. 14 , the displacement device 70 can comprise an actuation device 73. In particular, the actuation device 73 can be an actuator, for example a pneumatic actuator, or a mechanical actuator, or an electromechanical actuator.

Preferably, the actuation device 73 can be a motor, in particular an electric motor 73, provided with a motor shaft (not shown in the figure) arranged to rotate about a rotation axis 173. The motor shaft of the motor 73 can be arranged to mesh with an endless screw 71 sliding along a sliding direction 171. More precisely, the endless screw 71 is pivotally connected at an engagement portion 76 to an actuation portion 75 integral to said fixed tubular body 25.

Therefore, to cause a rotation of the fixed tubular body 25 in a first sense, in particular in the sense opposite to the sense of rotation 110 of the tubular body 10, the motor 73 is operated in such a way to cause a rotation of the motor shaft about the rotation axis 173 in a first axis of rotation 172 (see FIG. 15 ). In this way, as anticipated above, the releasing point P2, in the case of FIG. 13 also the catching point P1, is positioned at an angular position upstream of the angular position of the reference catching point P2*. Therefore, the releasing instant tr is anticipated with respect to the reference instant tr* (see also FIG. 9 ).

Instead, to cause a rotation of the fixed tubular body 25 in a second sense of rotation, in particular in the sense consistent with the sense of rotation 110 of the tubular body 10, the motor 73 is operated in such a way to cause a rotation of the motor shaft about the rotation axis 173 in a second sense of rotation 172′ (see FIG. 17 ). In this way, as anticipated above, the releasing point P2, in the case of FIG. 15 also the catching point P1, is positioned in an angular position downstream of the angular position of the reference catching point P2*. Therefore, the releasing instant tr is postponed with respect to the reference instant tr* (see also FIG. 12 ).

In an alternative embodiment of the invention, instead of the motor 73, a linear electric actuator can be used i.e. an electric motor whose axis can slide instead of rotating. In this way it is possible to connect the axis of the electric motor directly at the engagement portion 76 to the actuation portion 75 integral to the fixed tubular body 25.

In particular, in the embodiments described above and shown in particular in the figures from 4 to 18, the suction chamber 20 is pneumatically connected to the suction holes 3 by a vacuum distribution device 50 equipped with the first and the second sealing member 27 a and 27 b radially oriented and positioned at opposite sides with respect to the, or each, aperture 26. More in particular, between the first and the second sealing member 27 a and 27 b is not present any other element that is able to close the suction holes 3. Therefore, the suction chamber is delimited by the first and the second sealing member 27 a and 27 b.

In the alternative embodiment diagrammatically shown in the FIGS. 19 and 20 , the aforementioned vacuum distribution device 50 comprises a fixed tubular body 25 coaxially mounted within of the tubular body 10 and pneumatically communicating with the device for generating a predetermined vacuum degree. More in detail, the fixed tubular body 25 is provided with at least one aperture 26 having a predetermined angular amplitude, in particular an angular amplitude corresponding to the length of the sheet, or of the panel, 5 to be processed, or to the portion of the path that the web or sheet, 5 covers on the roll.

The vacuum distribution device 50 comprises in this case a plurality of sealing members 27 integral and positioned longitudinally to the tubular body 10. More in particular, each sealing member 27 is associated to at least one row of suction holes 3 arranged to pneumatically connect the external surface 11 to the device for generating a predetermined vacuum degree through the aperture 26. Furthermore, between a sealing member 27 and the following sealing member 27 associated to two different suction groups 30, annular sealing members 28 can be provided. In this case, the displacement device 70 is, advantageously, configured to cause a rotation of the fixed tubular body 25 about the longitudinal rotation axis 101. More precisely, as shown, for example in detail in FIG. 20 , in order to anticipate the releasing instant tr of a sheet, or web, of paper 5 with respect to the reference condition tr*, the fixed tubular body 25 can be rotated in the sense opposite to the sense of rotation 110 of the tubular body 10. In this way, the releasing point P2 will be positioned, going in the sense of rotation 110, upstream of the angular position of the reference releasing point P2*, because the suction holes 3 will leave the web or sheet, 5 in advance with respect to the reference case (diagrammatically shown in figure with a broken line).

In the further alternative embodiment diagrammatically shown in FIG. 21 , analogously to what is described above with reference to the embodiments shown in the FIGS. 8, 11, 16 and 18 , a first and a second sealing member 27 a and 27 b are provided extending longitudinally to the tubular body 10 between the internal surface 12 and a fixed tubular body 25. In this case, however, at least one sealing member, for example the sealing member 27 b is mounted on a support 21 that can move with respect to the fixed tubular body 25, for example within a guide 22 peripherally made at the fixed tubular body 25. In this case, therefore, the displacement device 70 can be configured to move, in particular rotate about the longitudinal axis 101, the movable support 21.

In this way, it is possible to change only the releasing position P2, whilst the catching position P1 can be a fixed position and coincident with a reference angular position P1*.

Alternatively, a first and a second displacement device 70 a and 70 b can be provided, one configured to move the movable support 21 and the other configured to move the tubular body 25. In this way it is, therefore, possible to change the catching point and the releasing point P1 and P2 independently from each other (FIG. 22 ).

In an alternative embodiment of the invention that is not shown, it is possible to mount the first and the second sealing member 27 a and 27 b on two supports, that can move independently with respect to each other, to adjust the catching point and/or the releasing point P1 and/or P2 maintaining the fixed tubular body 25 fixed. In a further alternative embodiment of the invention, the displacement device 70 can comprise a linear actuator, in particular of mechanical, or electric, or electromechanical, or pneumatic, type arranged to cause the vacuum distribution device 50 to rotate against a movable abutment member. In this way, changing the position of the movable abutment member it is possible to adjust the angular position of the vacuum distribution device 50.

In the further embodiment diagrammatically shown in FIG. 23 , upstream of the folding or interfolding unit 150 according to the invention, a first and a second cutting roll 1 c and 1 d can be provided configured to cut a respective web of paper, respectively, in a predetermined first and second plurality of sheets of predetermined length. According to the present invention, also the first and the second cut roll 1 c and 1 d can be provided with respective displacement devices 70 c and 70 d configured to move, according to one of the embodiments described above with reference to the figures from 4 to 18 of the folding or interfolding rolls, a respective vacuum distribution device 50 in such a way to postpone, or anticipate, depending on the different aim, the releasing point P2, and, in case, also the catching point P1, of the respective processed web or sheet of paper.

It is possible to adjust the phase both of the first and of the second plurality of detaching fingers 40 a and 40 b, and of the position of the catching point P1 and/or of the releasing point P2 and with respect to the reference values and can be computed with respect to a stating condition and/or with respect to an operative condition of the machine 100. In the case that the aforementioned reference values are those of a starting condition of the machine, or point of zero, the reference points can be computed, preferably, in function of the paper weight, or of the size of the sheets 5. In addition to the change of the paper weight, or of the sheets, of paper 5 it is possible to change the function through which the instantaneous instants of the catching point P1 and/or of the releasing point P2 and/or the releasing instant tr of the detaching fingers 40 a, and 40 b are computed.

In the case that the reference values are referred to the state of the machine, i.e. to the moment in which the machine is in working conditions and, therefore, works at an instantaneous operating speed, or at a predetermined speed, the catching point P1 and the releasing point P2 and/or the releasing instant tr of the detaching fingers 40 a and 40 b are computed by the main control unit 300 through a determined algorithm. The computation can be of threshold speed type, i.e. it is possible to change the catching point P1 and/or the releasing point P2 when a predetermined operative speed is exceeded going up or down. In an alternative embodiment of the invention, it is possible to change the catching point P1 and/or the releasing point P2 starting from a starting value, or value of zero, computing these in function of the set, or the instantaneous, speed. The function linking the instantaneous speed and the position of points P1 and P2 can be of any kind, for example, linear, not linear, or other. Furthermore, the functions can be selected on the basis of the paper weight, or of the size of the sheets fitting the machine 100 to the type of paper, or of product. Analogously to the cases described above, it is possible to change the delay or the advance of the instants ta and tr of the detaching fingers 40 a, 40 b automatically fitting the machine 100 to the change of the operative conditions and/or of the type of product.

Even though in the FIGS. 1, 2 and 3 are not shown for clarity reasons, it is appropriate to specify that separation members of type known to the skilled person in the art can be, however, provided and configured to carry out the separation of a finished stack of folded or interfolded sheets 250 from the following forming stack 250.

The foregoing description exemplary embodiments of the invention will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such embodiment without further research and without parting from the invention, and, accordingly, it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realize the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation. 

1. A folding or interfolding unit of a web, or sheet, of paper, comprising: a first and a second folding or interfolding roll of a web or sheet of paper configured to fold or interfold said web or sheet of paper according to a predetermined folding or interfolding configuration at a folding or interfolding zone arranged between said first and said second folding or interfolding roll; a first and a second plurality of detaching fingers configured to cause said web or sheet of paper to be detached from an external lateral surface of the respective folding or interfolding roll; a first and a second actuation group configured, respectively, to cause a back-and-forth oscillatory motion of said first and second plurality of detaching fingers towards/from said folding or interfolding zone, in such a way to cause a respective web or sheet of paper to be detached, respectively, from said first and second folding or interfolding roll, said folding or interfolding unit being characterized in that said first and second actuation group are, furthermore, configured to postpone or anticipate said oscillatory motion, respectively, of said first and of said second plurality of detaching fingers with respect to a predetermined reference oscillatory motion, in such a way to delay or anticipate, the instant (tr) in which said first and second pluralities of detaching fingers are arranged to cause said web or sheet of paper to be detached, respectively, from said first folding roll and from said second folding roll.
 2. The folding or interfolding unit of a web, or sheet, of paper according to claim 1, wherein each said first and second folding or interfolding roll, comprises: a tubular body configured to rotate about a longitudinal rotation axis in a predetermined sense of rotation, said tubular body being provided with an external lateral surface and with an internal lateral surface pneumatically communicating with each other through a plurality of suction holes organized according to plurality of longitudinal rows; a suction chamber defined within said folding or interfolding roll and pneumatically connected to a vacuum generation device configured to generate a predetermined vacuum degree; a vacuum distribution device configured to selectively pneumatically connect said suction chamber with at least one row of suction holes of said plurality, at determined angular positions of said tubular body in such a way to cause the processed sheet or web of paper to be sucked, and to adhere at a corresponding portion of said external lateral surface of said folding or interfolding roll arranged between a catching point and a releasing point (P1,P2) having determined angular positions.
 3. The folding or interfolding unit of a web, or sheet, of paper according to claim 2, wherein a displacement device is, furthermore, provided configured to move said vacuum distribution device, in such a way to change the angular position of said catching point (P1) and/or of said releasing point (P2) of said web or sheet of paper, and, therefore, to anticipate, or postpone, the instant in which said web or sheet of paper adheres to or leaves said external lateral surface of said first, or second, folding or interfolding roll.
 4. The folding or interfolding unit of a web, or sheet, of paper, according to claim 3, wherein said displacement device is configured to move said vacuum distribution device during said rotation of said tubular body about said longitudinal rotation axis.
 5. The folding or interfolding unit of a web, or sheet, of paper, according to claim 3 wherein said vacuum distribution device comprises a fixed tubular body coaxially mounted within said tubular body, said fixed tubular body being pneumatically connected with said device for generating a predetermined vacuum degree and being provided with at least one aperture and wherein said displacement device is configured to cause a rotation of said fixed tubular body about said longitudinal rotation axis.
 6. The folding or interfolding unit of a web, or sheet, of paper, according to claim 3 wherein said displacement device comprises an actuation device selected from the group comprising: a linear actuator; a mechanical actuator; an electric actuator; an electromechanical actuator; a pneumatic actuator; or a combination thereof.
 7. The folding or interfolding unit of a web, or sheet, of paper, according to claim 5, wherein said vacuum distribution device comprises a first and a second sealing member integral to said fixed tubular body at opposite sides with respect to said or each aperture, said first and second sealing members being positioned longitudinally to said tubular body.
 8. The folding or interfolding unit of a web, or sheet, of paper, according to claim 2, wherein said vacuum distribution device comprises a plurality of sealing members integral to said tubular body and positioned longitudinally to the same, each sealing member of said plurality being associated to at least one row of suction holes arranged to pneumatically connect said external surface with said device for generating a predetermined vacuum degree.
 9. The folding or interfolding unit according to claim 1, wherein said first and second actuation group comprise, respectively: a first and a second motor group configured to cause a rotation of a first and of a second motor shaft about respective axes of rotation; a first and a second oscillator device configured to convert the rotational motion of said first and of said second motor shaft on an inlet axis, to an oscillatory motion on an outlet axis, to transmit said oscillatory motion to said first and to said second plurality of detaching fingers.
 10. The folding or interfolding unit according to claim 9, wherein said first and second motor group are, furthermore, configured to change the speed of rotation of said first and of said second shaft of rotation with respect to a reference speed of rotation (vm*) for a determined interval of time (Δt*), in such a way anticipate, or postpone, respectively, the oscillatory motion of said first and of said second plurality of detaching fingers.
 11. The folding or interfolding unit according to claim 10, wherein said first and second actuation groups comprise, respectively: a first and a second motor group configured to cause a rotation of a first and of a second motor shaft about respective axes of rotation; a first and a second oscillator device configured to convert the rotational motion of said first and of said second motor shaft to an oscillatory motion of said first and of said second plurality of detaching fingers; and wherein a first and a second adjustment device are, furthermore, provided respectively associated to said first and to said second oscillator device and configured to anticipate or postpone, the instant (tr) in which said first and second pluralities of detaching fingers are arranged to hit said web or sheet of paper to cause said web or sheet of paper to be detached, respectively, from said first and from second folding or interfolding roll.
 12. The folding or interfolding unit according to claim 11 wherein said first and second adjustment devices comprise, respectively, a first and a second phase-shifter gearbox.
 13. The folding or interfolding unit according to claim 12, wherein said first and second phase-shifter gearbox are, respectively, provided with a first and with a second epicycloidal gear, said first and second phase-shifter gearbox being operatively connected, respectively, to a first and to a second motor configured to operate, respectively, said first and second epicycloidal gear in such a way to accelerate, or decelerate, said oscillatory motion of said first and second pluralities of detaching fingers.
 14. The folding or interfolding unit of a web, or sheet, of paper, according to claim 4 wherein said displacement device and/or said first and second actuation group are configured to be operated by an operator through an interface panel, or HMI “Human Machine Interface”.
 15. The folding or interfolding unit of a web, or sheet, of paper, according to claim 14 wherein said displacement device and/or said first and second actuation group are operated by an electronic control unit as a function of at least one of the following parameters: instantaneous operating speed of the first and of the second folding or interfolding roll; length of the sheet of paper; paper weight.
 16. The folding or interfolding unit of a web, or sheet, of paper, according to claim 2 wherein said plurality of longitudinal rows of rows of suction holes are organized according to a plurality of suction groups, each suction group of said plurality comprising at least 2 longitudinal rows of holes close to each other.
 17. The folding or interfolding unit of a web, or sheet, of paper, according to claim 2 wherein said plurality of longitudinal rows of suction holes are organized according to a plurality of suction groups, each suction group of said plurality comprising at least 3 longitudinal rows of holes close to each other.
 18. The folding or interfolding unit of a web, or sheet, of paper, according to claim 16, wherein the distance between two following suction groups of said plurality is equal to the length of the processed sheet.
 19. The folding or interfolding unit of a web, or sheet, of paper, according to claim 12, wherein said first and second phase-shifter gearboxes are operatively connected, respectively, to said first and to said second motor group by a first and a second transmission belt.
 20. The folding or interfolding unit of a web, or sheet, of paper, according to claim 19, wherein said first and second phase-shifter gearboxes are, furthermore, operatively connected to a first and to a second actuation device by a first and a second transmission belt, said first and second actuation devices being arranged to transmit the rotational motion caused by said first and second motor groups, respectively, to said first and to said second oscillator device.
 21. The folding or interfolding unit of a web, or sheet, of paper, according to claim 20, wherein said first and second phase-shifter gearboxes are, respectively, provided with a first and with a second electric motor arranged to adjust the speed of rotation of said first and of said second actuation device.
 22. The folding or interfolding unit according to claim 9, wherein said first oscillator device and said second oscillator device are, respectively, provided with a first and a second desmodromic cam.
 23. The folding or interfolding unit according to claim 9, wherein said first and second oscillator devices are connected at respective first ends of said first and of said second transmission group, said first and second transmission groups being operatively connected, at a respective second end opposite to said first end respectively, to said first and to said second plurality of detaching fingers.
 24. A method for folding or interfolding, a web or sheet of paper in a paper converting machine comprising the steps of: feeding at least one web or sheet of paper along an advancing direction; folding, or interfolding, said web or sheet of paper at a predetermined folding or interfolding zone, of a paper converting machine, said folding or interfolding step, being carried out by a first and a second folding or interfolding roll at a folding or interfolding zone, defined between them; detaching by a first and a second plurality of detaching fingers said web or sheet of paper from the external lateral surface of the respective folding or interfolding roll, said detaching step being carried out causing a back-and-forth oscillatory motion of said first and second plurality of detaching fingers towards/from said folding or interfolding zone; said method being characterized in that an adjustment step is, furthermore, provided for adjusting the phase between said first and second pluralities of detaching fingers and said first and second folding or interfolding rolls, respectively, said adjustment step being arranged to delay or anticipate, said oscillatory motion of said first and second plurality of detaching fingers, in particular with respect to a predetermined reference oscillatory motion, in such a way to postpone or anticipate, at least the instant (tr) in which said first and second pluralities of detaching fingers are arranged to cause the detachment of said web or sheet of paper, respectively, from said first and from second folding or interfolding roll.
 25. The method for folding or interfolding a web or sheet of paper, according to claim 24 wherein said oscillatory motion of said first and second plurality of detaching fingers is adjusted by an electronic control unit as a function of at least one of the following parameters: instantaneous operating speed of the folding or interfolding roll; operative speed of the folding or interfolding roll; length of the sheet; paper weight.
 26. The method for folding or interfolding a web or sheet of paper, according to claim 25 wherein said electronic control unit automatically adjusts said oscillatory motion of said first and second pluralities of detaching fingers, or adjust said oscillatory motion of said first and second pluralities of detaching fingers on the basis of a command received by an interface panel or HMI (Human Machine Interface). 